JOSEPH HENRY 201 



ment being completed, I stationed myself near the galvanometer and 

 directed an assistant at a given word to immerse suddenly, in a vessel 

 of dilute acid, the galvanic battery attached to the magnet. At the 

 instant of immersion, the north end of the needle was deflected 30° 

 to the west, indicating a current of electricity from the helix surround- 

 ing the armature. The effect, however, appeared only as a single 

 impulse, for the needle, after a few oscillations, resumed its former 

 undisturbed position in the magnetic meridian, although the galvanic 

 action of the battery, and consequently the magnetic power, was still 

 continued. I was, however, much surprised to see the needle suddenly 

 deflected from a state of rest to about 20° to the east, or in a con- 

 trary direction when the battery was withdrawn from the acid, and 

 again deflected to the west when it was re-immersed. This operation 

 was repeated many times in succession, and uniformly with the same 

 result, the armature the whole time remaining immovably attached to 

 the poles of the magnet, no motion being required to produce the 

 effect, as it appeared to take place only in consequence of the instan- 

 taneous development of the magnetic action in one, and the sudden 

 cessation of it in the other. 



This experiment illustrates most strikingly the reciprocal action of 

 the two principles of electricity and magnetism, if indeed it does not 

 establish their absolute identity. In the first place, magnetism is de- 

 veloped in the soft iron of the galvanic magnet by the action of the 

 currents of electricity from the battery, and secondly, the armature, 

 rendered magnetic by contact with the poles of the magnet, induces in 

 its turn currents of electricity in the helix which surrounds it ; we have 

 thus, as it were, electricity converted into magnetism and this magnet- 

 ism again into electricity. 



Another fact was observed which is somewhat interesting, inas- 

 much as it serves in some respects to generalize the phenomena. Af- 

 ter the battery had been withdrawn from the acid, and the needle of 

 the galvanometer suffered to come to a state of rest after the resulting 

 deflection, it was again deflected in the same direction by partially de- 

 taching the armature from the poles of the magnet to which it con- 

 tinued to adhere from the action of the residual magnetism, and in 

 this way, a series of deflections, all in the same direction, was pro- 

 duced by merely slipping off the armature by degrees until the contact 



